(a) Field of the Invention
The present invention relates to a switch controller, a switch control method, and a converter using the same, and more particularly, to a power factor correction switch controller, a power factor correction switch control method, and a converter using the same.
(b) Description of the Related Art
A converter receives power and supplies the power to the target load. The input power is alternating current (AC) voltage, and the output power supplied to the load is direct current (DC) voltage. As the current flowing along the load is similar to the input power current, a phase difference occurs between the input power voltage and the input power current, and causes power loss. In case the load connected to the output terminal of the converter is an LED light source including a plurality of LEDs and a DC current flows to the respective LEDs, a power loss occurs due to the phase difference between the input power voltage and the input power current so that the power factor is lowered.
In order to improve the power factor, the phase difference between the input power voltage and the input power current should be reduced. The input power current is influenced by the current flowing along the load. For this reason, when the current supplied to the load involves a frequency and a phase similar to those of the input power voltage, the phase difference between the input power current and the input power voltage can be reduced.
Furthermore, it is necessary in improving the total harmonic distortion (THD) to make the input power current bear a sine curve. The power switch of the converter may interfere with other equipment due to the switching operation thereof. In order to minimize such interference, the harmonic component of the input power current should be small. The THD is to digitize the amount of harmonics, and it is required in reducing the THD to approximate it to the single frequency sine curve. That is, in order to improve the power factor and the THD, the current supplied to the load should be in the form of a sine curve, and should have a frequency and a phase similar to those of the input power voltage.
With the conventional converter, the input AC power is full-wave rectified so as to generate an input voltage, and the input voltage is sensed so as to generate a reference signal. The reference signal and the current flowing along the load are compared with each other, and the current flowing along the load is controlled in dimension in accordance with the reference signal. As the reference signal is altered depending upon the input voltage, the current flowing along the load is also altered in dimension depending upon the reference signal. Accordingly, the current supplied to the load involves a frequency and a phase that are approximated to those of the input power voltage. Furthermore, the input power current has a similar form to the sine curve. However, in case a resistor is used to sense the full-wave rectified input power voltage, it is difficult to integrate a control unit for controlling the converter. The reason is that the input power voltage is commonly high, and it is difficult to integrate the high voltage-endurable resistor. Furthermore, power consumption separately occurs at the resistor.
A separate power factor correction controller circuit may be used to correct the power factor in a different manner. However, in this case, an additional element is needed to serve the power factor correction controller circuit so that the production cost increases, and it becomes difficult to realize the required integration.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.